Tar sands, also known as oil sands and bituminous sands, are siliceous materials impregnated with petroliferous material convertible to petroleum products. The largest and most important deposits of the sands are the Athabasca sands found in northern Alberta, Canada. These sands underlay more than 1300 square miles at a depth of 0 to 2000 feet. The tar sands are primarily silica, closely associated with petroliferous material (heavy oily material) which varies from about 5 to about 21 percent by weight, with a typical content of 13 weight percent comprising sand. The oil is quite heavy, 6.degree. to 8.degree. API gravity and contains typically 4.5 percent sulfur and about 38 percent aromatics. The sands include clay and slit in quantities of from 1 to 50 weight percent (more usually 10 to 30 percent) and water in quantities of 1 to 10 percent by weight. The recovery of oily product from the tar sand has been pursued by a "cold water process," a "hot water process" as well as by retort methods which are akin to thermal cracking or pyrolysis techniques as used to process oil shale. A thermal method of recovering bitumen by direct retorting has been studied since 1940. In direct retorting, the raw oil sand is contacted with spent sand and fluidized by reactor off gas at a temperature above 900.degree. F. The volatile products are flashed while 6-7 weight percent of coke (based on bitumen) is deposited via thermal cracking. The coked sand is burned off in a separate unit at 1200.degree.-1400.degree. F. and recirculated. The voluminous amount of spent sand needed, i.e., 5-10 parts per part of cold tar sand, for the process necessitates a very large retort volume per barrel of recoverable oil. Such methods obviously are expensive and of little interest. Serious waste heat and handling problems arise with this process.
The present invention is concerned with a combination process which embodies the technique of low temperature thermal distillation of bitumen in the presence of recycled hot sand particles acquired from a fuel gas generation zone processing a solvent extracted sand residue material of a solvent extraction operation.
The processing of sand comprising residue hydrocarbonaceous material recovered from a low temperature-severity distillation operation and subsequent solvent extraction thereof is accomplihed under relatively high temperature conditions in the presence of a gas stream comprising oxygen and steam in desired proportions to produce particularly fuel gas. Thus, the reactions that occur in the gasification of the hydrocarbonaceous residue material include thermal cracking in combination with different other reactions, such as:
(1) C+O.sub.2 .fwdarw.CO.sub.2
(2) C+CO.sub.2 .fwdarw.2CO
(3) C+H.sub.2 O.fwdarw.CO+H.sub.2
(4) C+2H.sub.2 .fwdarw.CH.sub.4
(5) CO+H.sub.2 O.fwdarw.CO.sub.2 +H.sub.2
(6) H.sub.2 +1/2O.sub.2 .fwdarw.H.sub.2 O
The oxidation of carbon, reaction (1), is highly exothermic. Gasification processes use partial oxidation of char with either air or oxygen to provide heat for the endothermic reactions of (2) and (3). These reactions comprising the gasification of char with CO.sub.2 and the water gas reaction (3) are thermodynamically favored at temperatures above 1350.degree. F. The methanation reaction (4) is highly exothermic and is thermodynamically favored at temperatures less than 1150.degree. F. The water gas shift reaction (5) is mildly exothermic with favorable equilibrium below 1350.degree. F. It is recognized by those skilled in the art that the composition of the produced fuel gas may be varied with pressure and temperature. That is, by raising the pressure and lowering the temperature, the methane yield may be increased. On the other hand, fuel gas of at least 120 BTU/SCF does not necessarily require the presence of large amounts of methane.